This application claims priority to JP 11-02278 filed Jan. 29, 1999 in Japan.
This invention relates to a fuel cell and a separator and, more particularly, to a fuel cell having a fluid duct passed through by a fluid containing an active material, and a separator therefor.
A fuel cell generating electricity by fuel is available on the market. This fuel cell has plural unit cells, each having electrodes sandwiching an electrolyte membrane in-between, and a plurality of separators arranged between the unit cells for partitioning the unit cells from one another. The separator is routinely formed with a fluid duct for guiding an active material containing fluid, supplied from a fluid inlet, towards a fluid outlet. In JP Patent Kokai JP-A-5-251097, there is disclosed a fuel cell in which plural fluid ducts passed through by the active material containing fluid are arranged sideby-side and in which the duct width of a portion of the fluid duct lying closer to the fluid inlet is set so as to be broader than that of the fluid duct portion lying closer to the fluid outlet. It is explained in the Publication that this structure is used in expectation of water droplets falling under the effect of gravity.
In JP Patent Kokai JP-A-10-106594, there is disclosed a separator comprised of plural grooved fluid ducts, arranged side-by-side, and through which flows an active material containing fluid. These fluid ducts are provided with a separator intermediate between the fluid inlet and the fluid outlet. In this separator, the fluid ducts are of the same width throughout the entire length of the fluid ducts.
In the above-described fuel cell, plural contact lugs 210 formed on a separator 200 face an electrode 100 and are contacted therewith at a pre-set contact width, as shown in FIG. 9. In this separator 200, a fluid duct 230 is formed in such a manner that the spacing between neighboring contact lugs 210 represents the duct width. Thus, the active material containing fluid, supplied from the fluid inlet, is guided along the fluid duct 230 towards the fluid outlet.
In the separator 200, the contact lugs 210 face and contact with the electrode 100 at a pre-set contact width. Since the portion of the electrode 100 contacted with the contact lugs 210 is not directly facing the fluid duct 230, dispersion of the active material into the inside of the electrode 100 is limited. That is, the contact portion of the electrode 100 with the contact lugs 210 constitutes a diffusion limiting portion PM.
Also, in the fluid duct 230 of the fuel cell, the active material is consumed as the fluid duct proceeds along a direction proceeding from the upstream side to the downstream side, that is from the fluid inlet towards the fluid outlet. The result is that, on the downstream side of the fluid duct, that is on the side of the fluid duct towards the fluid outlet, the active material concentration of the active material containing fluid tends to be lowered.
In view of the above depicted status of the art, it is an object of the present invention to provide a fuel cell and a separator for a fuel cell in which dispersion or diffusion of an active material in the active material containing fluid into the inside of the electrodes on a side closer to the downstream side of the fluid duct, that is on the fluid outlet side, is advantageously facilitated.
The present inventor has conducted perseverant searches for developing an improved separator for a fuel cell and arrived at a concept that, if the contact width of the contact lugs on a downstream side of the flow duct, that is on a side closer to the fluid outlet, is set smaller than the contact width of the contact lugs on a side closer to the fluid inlet, internal diffusion to the electrode on the downstream side can be more uniform to improve the power generating performance on the downstream side. This concept has led to completion of the present invention.
(i) According to a first aspect of the present invention, a fuel cell has a plurality of unit cells each including electrodes sandwiching an electrolyte membrane in-between, and a plurality of separators each arranged between the unit cells. The separator has a plurality of juxtaposed contact lugs facing the electrodes and contacting the electrodes at pre-set contact widths and a plurality of fluid ducts each having a space between neighboring ones of the contact lugs as a duct width and each being configured for guiding a fluid containing an active material supplied from a fluid inlet towards a fluid outlet. In the separator, the contact width of the contact lugs on a side of the fluid duct closer to the fluid outlet is set smaller than that of the contact lugs on a side of the fluid duct closer to the fluid inlet.
(ii) According to a second aspect of the present invention, there is provided a separator for use in a fuel cell having a plurality of unit cells each including electrodes sandwiching an electrolyte membrane in-between and a plurality of separators each arranged between the unit cells has a plurality of juxtaposed contact lugs facing the electrodes and contacting the electrodes at pre-set contact widths and a plurality of fluid ducts each having a spacing between neighboring ones of the contact lugs as a duct width and each being adapted for guiding a fluid containing an active material supplied from a fluid inlet towards a fluid outlet. In the separator, the contact width of the contact lugs on a side of the fluid duct closer to the fluid outlet is set smaller than that of the contact lug on a side thereof closer to the fluid inlet.
(iii) According to a third aspect of the present invention, in the separator, there is provided an area in which the contact width of contact lugs on a side of the fluid duct closer to the fluid outlet is set smaller than that on a side thereof closer to the fluid inlet. Thus, on the downstream side of the fluid duct, that is on the side of the fluid duct closer to the fluid outlet, the ratio of contact of the contact lugs of the separator with the electrodes becomes smaller such that the area for each diffusion limiting portion is smaller. The result is that the active material can be dispersed and diffused more evenly into the inside of the electrode on the downstream side of the fluid duct, that is on a side closer to the fluid outlet.